Vehicles may experience fluctuation in engine torque, manifested as a vehicle oscillation, and which may be referred to as surge. Surge may be caused by poor combustion stability due to a variety of engine operating conditions, including air-fuel ratio, burnt gas amount, fueling, and ignition timing. Poor combustion stability may be caused or aggravated by changes in environmental factors including ambient temperature, altitude, humidity, and others.
One example approach for addressing surge in a lean burn engine adjusts air-fuel ratio. For example, in U.S. Pat. No. 5,857,445, the engine control is switched from a lean combustion state to a stoichiometric combustion state in response to surge. In particular, changes in engine speed provide a surge index, which is then used to adjust the fuel injection amount, and thus the air-fuel ratio.
However, the inventors herein have recognized disadvantages with such an approach. For example, surge conditions may be initiated due to degraded feedback knock control, where spark timing is adjusted responsive to a knock indication. Specifically, the engine controller may identify knock via a knock sensor, and retard spark timing in response thereto in order to abate engine knock. However, once the knock is abated, the engine controller may advance spark timing. Under some conditions, the spark timing may be advanced too quickly, or too far, thus again generating knock. This feedback cycle may repeat, thus generating vehicle surge conditions. Additionally, simply operating with excessive spark retard, such as during cold conditions for catalyst warm-up, may also result in engine surge.
In one approach, the above issues may be addressed by a method for operating an engine of a vehicle, the engine having a combustion chamber, comprising: controlling a stability of the vehicle in response to a vehicle acceleration; and adjusting spark timing in the combustion chamber of the engine in response to a knock indication, and further adjusting spark timing in response to the vehicle acceleration to reduce surge. In another approach, the method may include controlling a stability of the vehicle in response to a vehicle longitudinal acceleration indicated from an accelerometer coupled in the vehicle; retarding spark timing in the combustion chamber of the engine from peak torque timing in response to an operating condition; and when vehicle surge is identified by the vehicle acceleration from the accelerometer, advancing spark timing.
In this way, it is possible to take advantage of the acceleration information for both stability control and spark-timing induced surge control. Further, by appropriately adjusting spark timing under appropriate surge conditions as indicated by the vehicle acceleration, surge may be addressed. For example, by adjusting spark timing in response to acceleration to reduce surge when performing feedback knock control, it is possible to compensate for surged induced by the feedback knock control. As another example, by advancing spark timing in response to the vehicle acceleration, it is possible to compensate for effects surge caused by spark retard.
It should be understood that the summary above is provided to introduce in simplified form a selection of concepts that are further described in the detailed description. It is not meant to identify key or essential features of the claimed subject matter, the scope of which is defined uniquely by the claims that follow the detailed description. Furthermore, the claimed subject matter is not limited to implementations that solve any disadvantages noted above or in any part of this disclosure.